1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a package structure including a lead base and a cap. The method according to the present invention is applicable to the production of IC packages in the form of, for example, a pin grid array (PGA), a dual in line package (DIP), and a leadless chip carrier (LCC).
2. Description of the Related Arts
In general, a lead base for a semiconductor device having a package structure is made of highly heatproof thermosetting plastics such as heatproof epoxy resin, bismaleimide-triazine resin (BT resin) or polyimide resin. The lead base has a square shape in plan view, and a groove for mounting a semiconductor chip is provided in the center of the lead base. A barrier for preventing sealing plastics from reaching the side portion of the lead base is provided on the top surface of the lead base. Pins are provided at the bottom of the lead base, and these pins are connected to the semiconductor chip through wires.
In the production of the package structure, a liquid plastic for filling is disposed within a barrier on the top surface of the lead base including the groove, and the disposed filling plastic is hardened by curing. A thermosetting plastic solution such as an epoxy resin solution is used as the filling plastic, and the curing is carried out by raising the temperature.
Then, a thermosetting plastic solution for fixation similar to the filling plastic is disposed in the upside-down turned cap. The depth of the plastic solution for fixation becomes uniform with a lapse of time, and the device is turned upside-down and is fitted into the cap containing the plastic solution for fixation.
Then, the plastic solution for fixation is hardened by curing at an elevated temperature to fix the cap to the device, and thus a package is produced.
However, a problem in the prior art production of the package structure is that the step of making the depth of the plastic solution for fixation uniform with a lapse of time is troublesome, a perfect uniformity of the depth of the plastic solution for fixation is difficult to realize, and voids are apt to be generated in edge portions, which voids reduce the effective length of the water creepage path and thus deteriorate the waterproofing characteristic. If such a water creepage occurs, a conductor in the electrical circuit of the device may be blown, and if water creeps into the voids in the edge portions, a leakage of current or a short-circuit may occur.
There is also a problem in that creeping of melted solder into the voids may occur, and there is a further problem in that the hardened plastic for fixation between the cap and the lead base may be forced out, to deteriorate the quality of the package structure as a product.